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CDC: West Nile Virus Basics

Information on the virus, prevention, case information, and reporting dead birds

Maryland Department of Health and Mental HygieneProvides information on the West Nile virus in Maryland. You can also report online any dead birds found.

Mosquito Repellents:

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Facts about the West Nile Virus

What is it?

It is a virus which is typically carried by certain infected mosquitoes. It can cause meningitis and encephalitis (inflammation of the brain).

 

It was first isolated and identified in 1937 in Uganda. It made its first known appearance in the United States in 1999 in New York.

 

How is it transmitted?

 

The virus is transmitted by mosquitoes. Mosquitoes get it from feeding on infected birds.

 

There is no evidence that humans can transmit it to each other through casual contact. There is also no evidence that humans can acquire the West Nile virus infection from infected birds.

 

What are the symptoms?

 

Most patients have NO symptoms or have only very mild self-limited symptoms. Mild symptoms may include fever, headache, and/or body-aches. These symptoms usually go away without any treatment. 

 

In some individuals, particularly elderly persons, the West Nile virus has been known to cause severe disease such as meningitis or encephalitis. 

 

The biggest risk factor for developing severe disease from the West Nile virus is advanced age. Elderly individuals are at greatest risk.

 

How is it treated?

 

There is no specific medicine or treatment for West Nile virus infection. Symptoms usually go away without any medical treatment. 

 

In severe cases, it is generally managed with supportive care.

 

No vaccine is available at present.

 

What are the risks of being severely infected by West Nile virus?

 

Very small...

In areas where the West Nile virus is found, <1% of people who are bitten by an infected mosquito actually develop severe symptoms. 

 

How can this be prevented?

 

The best way to avoid the West Nile virus is to avoid being bitten by mosquitoes.

• Stay indoors at dusk, dawn, and early evening. 

• Get rid of standing pools of stagnant or still water. 

• Wear long sleeves and longs pants when outdoors.

• Spray insect repellent on exposed skin and clothing. 

• Use products containing the chemical DEET (N,N-diethyl-3-methylbenzamide). Of all the commercially available insect repellents, DEET has been found to provide the longest lasting protection against mosquito bites. Do not use repellents with more than 10% DEET on children.

Should I see a physician if I have been bitten by a mosquito?

 

No. The risks of acquiring West Nile Virus infection are very SMALL. Very few mosquitoes are actually infected with the virus. 

 

However, do seek medical attention, if you develop these symptoms:

• severe headache

• fever

• confusion

• muscle weakness and body aches

• stiff neck

• sensitivity of eyes to bright lights

References:

Petersen L, Martin A. West Nile virus: a primer for the clinician. Annals of Internal Medicine. 2002;137:173-179.

 

last updated 11/29/2006

 

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